Arterial endothelial cell cultures (human, bovine, porcine and canine) will be characterized further in terms of their growth characteristics and factors that affect their proliferation and mitogenesis. The effects of pH, divalent cations and plasma proteins on in vitro platelet-endothelial cell interaction will be examined. Studies on the isolation and characterization of the endothelial produced microfilaments to which platelets attach, are continuing as are the studies on the nature and composition of the basement membrane. Finally, these studies will be supplemented by studying the reaction and factors involved in the uptake and release of biogenic amines in cultured endothelial cells.